26 



The National Geographic Magazine 



"The Ugly Duckling" 



A raft supported upon metallic cylinders and propelled by aerial propellers. Above illustration 

 shows raft propelled by small gasoline motor. In subsequent experiments referred to in tlie 

 text, the bridge, or truss, supporting the propellers was raised considerably above the level of 

 the platform, and the engine employed was a four-cylinder water-cooled marine motor weigh- 

 ing 650 pounds. This caused the metallic floats to be sunk to their middle points ; but the 

 floats were not connected together at their ends, as shown above 



greater slip of the propellers acting in a 

 calm. I am inclined to think, however, 

 that this explanation is insufficient, and 

 would suggest the following as more 

 probable : 



The enormous mass of the moving 

 body enables it to acquire very consider- 

 able momentum with slight velocity, 

 whereas the opposing current of air has 

 stich slight mass that it cannot acquire 

 an equal momentum with a very much 

 higher velocity. 



If two bodies of unequal mass, moving 

 with equal but opposite velocities, come 

 into collision with one another, then the 

 heavier body will not be completely 

 stopped by the lighter. It will make head- 

 way against the resistance of the other, 

 even though the lighter should possess 

 superior velocity, provided, of course, 

 that it has a sufficient superiority of 



mass. We are here dealing with mo- 

 mentum {mv) , not velocity {v) alone. 

 The body having the greatest momentum 

 will be the victor in the struggle, what- 

 ever the actual velocities may be. 



The suggestiveness of this result lies 

 in its application to the ilying-machine 

 problem. A balloon, on account of its 

 slight specific gravity, must ever be at 

 the mercy of the wind. In order to make 

 any headway against a current of air, it 

 must itself acquire a velocity superior to 

 the wind that opposes it. On the other 

 hand, it is probable that a flying-machine 

 of the heavier-than-air type, at whatever 

 speed it moves, will be able to make 

 headway against a wind of much greater 

 velocity, provided its momentum is 

 greater than the momentum of the air 

 that opposes it. 



